Modern electronic vehicle brake systems, such as ABS or EBS brake systems, have a device for reducing yawing moments on the front axle in order to make the vehicle controllable on μ split as well. Fundamentally, yawing moments, which are brought about by different rolling friction or static friction between the running wheels of a vehicle and the surface on which it moves, lead to the vehicle deviating laterally from the desired direction of travel. Yawing moments can lead to the vehicle skidding in particular during braking in bends.
Efforts are therefore made always to ensure sufficient vehicle stability in the development of brake systems, for example pneumatic, hydraulic or hydraulic/pneumatic brake systems, and to stabilize the vehicle by adapted brake pressures. The pressure difference permissible on a vehicle axle between the brake cylinders for the running wheels of this axle is as a rule a compromise between controllability and steerability of the vehicle. It is generally the case that an empty vehicle with a short wheelbase is more critical to control than a vehicle with a long wheelbase. As the pressure difference between the brake cylinders concerned which is permissible in a brake system used in various vehicle types has to be geared to the critical vehicle type, the possible brake pressures are not utilized in a vehicle with a long wheelbase when this brake system is used.
A brake system for vehicles, in particular for utility vehicles, in which a sensor is provided for sensing a physical quantity which occurs when a brake pressure defined by the driver is applied, is discussed in German Patent Document No. 199 39 035 A1, for example. In this brake system, a hydraulic/pneumatic converter is provided, which is connected to an ABS valve and converts a brake pressure applied pneumatically to the converter into a hydraulic brake pressure for a vehicle brake. The sensor is integrated into the converter and responds and generates a warning signal when a pneumatic piston of the converter is in a stop position when the pneumatic/hydraulic converter is ventilated.
U.S. Pat. No. 4,872,729 discusses a brake system for a motor vehicle with a device for measuring the slip on the rear axle and a control device for influencing the brake pressure on the front wheels which limits the brake pressure on the front wheels depending on the measured slip on the rear axle.